1. The Field of the Invention
The present invention relates to a high aspect-ratio contact in a semiconductor device and a method of forming the same. In particular, the present invention relates to formation of a contact in a semiconductor device with a refractory metal and a refractory metal nitride liner that assists in filling of a contact hole in which the contact is situated. More particularly the present invention relates to an aluminum or aluminum alloy filled contact plug that fills a contact hole in a semiconductor device that is lined with a titanium layer and at least one titanium nitride layer. The titanium and the first of the at least one titanium nitride layers are formed by chemical vapor deposition. Subsequently formed titanium nitride layers, if any, are formed by physical vapor deposition (PVD).
2. The Relevant Technology
In the microelectronics industry, a substrate refers to one or more semiconductor layers or structures which includes active or operable portions of semiconductor devices. In the context of this document, the term xe2x80x9csemiconductor substratexe2x80x9d is defined to mean any construction comprising semiconductive material, including but not limited to bulk semiconductive material such as a semiconductive wafer, either alone or in assemblies comprising other materials thereon, and semiconductive material layers, either alone or in assemblies comprising other materials. The term substrate refers to any supporting structure including but not limited to the semiconductive substrates described above.
In the fabrication of semiconductor devices, metal contacts are formed over semiconductor substrates that have been processed to form devices connected to each other to form integrated circuits. In particular, aluminum and aluminum alloy lines have been deposited into vias and other recesses such as trenches and contact corridors. This method of metallization is used generally in the microelectronics industry. However, as devices have been miniaturized, due to requirements for a higher device density on a semiconductor substrate and a smaller device, the recesses to be filled have higher aspect ratios, where an aspect ratio is the depth of the recess divided by the width thereof.
One need for higher aspect ratio recesses is the formation of deeper contacts where, for example, a stacked capacitor for a dynamic random access memory (DRAM) is formed and then covered over by a dielectric layer. For such as a stacked DRAM capacitor, a contact with an aspect ratio greater than 5:1 would need to be formed in two steps using known prior art processes. Such prior art processing produces a conductive structure having two interconnect halves with a physical seam therebetween. Typically, the two interconnect halves have a width or cross-sectional footprint of about 0.35 microns or smaller. Alignment of the small footprint interconnect halves is problematic at best, and fabrication yield with such a process prerequisite is undesirable. Also undesirable is an increased resistivity caused by the physical seam between the two interconnect halves.
Difficulties have been encountered in depositing aluminum lines and contacts by conventional sputtering processes when submicron high aspect ratio recesses are to be filled. As a recess is made smaller and deeper (i.e. higher aspect ratio), the bottom and sides of the recess will receive less sputtered target material than the opening to the recess. Additional sputtering will result in a detrimental phenomena known as bread loafing where a layer of sputtered target material closes off the opening to the recess. Thus over time, the bottom and sides of the recess receive inadequate amounts of the sputtered metal material and the sputtered metal material overhangs and closes over the opening to the recess before the recess is substantially filled.
While the aluminum and the silicon in the semiconductor substrate must be electrically connected, it has become useful to use intermediate layers to provide better electrical connection to the silicon, and to provide a metallurgical barrier between silicon and aluminum to prevent spiking of the aluminum into the silicon. Spiking can interfere with the performance and reliability of the integrated circuit. Conventionally, one method which has been used to accomplish the metallurgical barrier has been to form a layer of titanium over a semiconductor substrate at the interconnect-exposed site. Titanium silicide is then formed at the interconnect-exposed site, and a titanium nitride layer is formed elsewhere, in that the titanium layer is exposed to a nitrogen atmosphere. While this method forms a metallurgical barrier between silicon and aluminum to prevent spiking, it often is inadequate to form the titanium nitride barrier because of the competing simultaneous formation of titanium silicide and titanium nitride at the titanium region that covers the exposed semiconductor substrate site.
One prior art solution to this inadequate prior art method has been to form the titanium silicide barrier layer first and then to sputter additional titanium nitride over the titanium silicide or titanium silicide/titanium nitride layer. In this way, a sufficient thickness of titanium nitride may be formed to provide a desired thickness in a barrier layer.
As stated, sputtered layers of titanium nitride have been used in integrated circuits as barrier layers for recesses such as contact holes, vias, and interconnects. Sputter deposited titanium nitride, however, is not very conformal and its step coverage within high aspect ratio recesses is poor. As such, there results an unacceptably thin or discontinuous titanium nitride barrier layer for a high aspect ratio recess.
As aspect ratios have been increasing for recesses in microelectronic devices, the need for substantial recess filling with sputtered aluminum and aluminum alloy metallization material has proved inadequate in spite of improved titanium nitride barrier layers. While high pressure and/or high temperature aluminum reflow recess filling techniques have been developed, a substantially filled recess having an aspect ratio exceeding 5:1 has been difficult or impractical to achieve.
It has been proposed to form a titanium nitride layer in the recess by chemical vapor deposition (CVD), for example by using titanium tetrachloride (TiCl4) in the presence of NH3, H2, and Ar. Although the TiCl4 CVD process has improved reflow techniques, substantially filled recesses with aspect ratios greater than about 5:1 have been elusive. One problem that has been experienced is that aluminum reflow requires a substantially pristine refractory metal nitride surface, whereas interstitial titanium nitride layer impurities incident to the TiCl4 CVD process have caused the aluminum to become impure. As a result, aluminum loses its relatively low-friction flowing or sliding ability over the impure titanium nitride layer.
Methods have been proposed to drive the interstitial impurities out of the titanium nitride layer by using thermal energy, but the thermal limit or budget of the fabrication process must be monitored so as avoid a yield decrease. Additionally, it has been observed that a thermal cleansing of the titanium nitride layer leaves significant voids in the titanium nitride layer that also resists flow of the aluminum there across. Attempts have been made to xe2x80x9cstuffxe2x80x9d the interstices in the titanium nitride layer with nitrogen. Even with a stuffing technique, however, substantially filled recesses with aspect ratios that exceed 5:1 are not readily realized.
What is needed is a method of lining and substantially filling a high aspect ratio recess with aluminum metallization or equivalents in microelectronic device fabrication where the aspect ratio of the recess exceeds 5:1. What is also needed is a method of forming a high aspect ratio structure that allows for a taller microelectronic component, such as a taller stacked DRAM capacitor, where the interconnect to the stacked DRAM capacitor is unitary and formed by a single recess filling process.
The present invention relates to a substantially filled recess in a semiconductor structure, where the recess has a height-to-width aspect ratio in a range from about 6:1 to about 10:1, and where the width is about 0.35 microns or smaller. The process steps and achieved structure in accordance with an embodiment of the invention comprise an interconnect in a recess having an aspect ratio that exceeds about 6:1. The recess, for example, can be a via, a trench, a contact corridor, or a combination thereof. In a first embodiment of the present invention, the recess is a contact hole that is substantially filled by first performing a surface pre-cleaning of the contact hole followed by degassing. Following degassing, a refractory metal layer is formed, and a refractory metal nitride layer is formed on the refractory metal layer. A heat treatment step, preferably by rapid thermal processing (RTP), is used to secure a refractory metal silicide contact upon semiconductor material such as silicon at the bottom of the contact hole.
At least two alternative methods may be carried out after heat treatment. In a first alternative, a high-temperature NH3 treatment is carried out to remove undesirable impurities within the contact hole and to replace the impurities in the refractory metal nitride layer with more nitrogen. In the second alternative, a second refractory metal nitride layer is formed by PVD upon the first refractory metal nitride layer. In either alternative, a metallization layer is deposited within the contact hole. Preferably, aluminum is used in a fast metallization deposition technique and alternatively by use of elevated temperatures to substantially fill the contact hole with aluminum. High pressure and temperature can also be used in combination in the inventive method to substantially fill the contact hole with aluminum.
In yet another embodiment of the present invention, the steps of precleaning, degassing, and deposition of a refractory metal layer are accomplished as set forth above. Deposition of the first refractory metal nitride layer is accomplished using trimethylethylenediamine tris (dimethylamino) titanium (TMEDT). Use of TMEDT allows for a higher density of titanium and nitrogen to form in the contact hole than that achieved in previous metal-organic deposition techniques. The aspect ratio achieved by a TMEDT-deposited refractory metal nitride layer and the subsequent deposit on of a second refractory metal nitride layer by PVD may exceed 8:1.
Following filling of the contact hole, residual surface metallization may be entirely removed by such techniques as etchback or by a planarization technique such as chemical mechanical planarization (CMP). Partial CMP of the surface metallization may be carried out, wherein a portion of the surface metallization remains to be patterned and treated to form metallization lines. CMP of the surface metallization assists in preventing unwanted reflective characteristics.
These and other features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.